Anti-terrorism officers in London yesterday arrested nine more suspects in connection with the attempted transit attack there July 21, while U.S. and British authorities negotiated over how to handle another bombing suspect who was arrested last week in Zambia, U.S. and British officials said.

Haroon Rashid Aswat, a British national of Indian descent, is in Zambian custody. He was detained while crossing into Zambia from neighboring Zimbabwe, according to the officials, who spoke on the condition of anonymity because the terrorism investigation is continuing.

The U.S. and British governments had been searching for Aswat since the deadly July 7 London transit bombings. At least 20 calls were made between a cell phone linked to Aswat and some of the suicide bombers.

Aswat had also long been sought by the FBI in connection with the U.S. criminal case against a fiery British imam, Abu Hamza Masri, which includes an alleged effort to set up a terrorist training camp in Oregon. A source said yesterday that the British opposed an effort to arrest Aswat about a month before the July 7 bombings.

The FBI had requested Aswat's arrest after locating him in South Africa but the British government blocked the effort, a U.S. law enforcement official said. The request was reported by CNN.

A spokesman for the British Embassy in Washington declined to comment on the allegation.

In London, with only one of four suspects in the failed July 21 bombing attempts in custody, thousands of police officers flooded the streets to calm a jittery public as authorities warned that more attacks are possible. Officials said the operation was one of the largest deployments of police officers since World War II.

Metropolitan Police Commissioner Sir Ian Blair said the operation was aimed at "trying to ensure the safety of Londoners" but warned that it was "a race against time" as police attempted to locate the remaining bombing suspects, according to the Associated Press.

"It does remain possible that those at large will strike again," Blair said. "It does also remain possible that there are other cells who are capable and intent on striking again."

With yesterday's pre-dawn arrests of nine men in the Tooting neighborhood of south London, 20 suspects are in British custody in connection with the July 21 attacks. No one was killed in those attempted strikes because the bombs did not detonate. Fifty-six people, including the four bombers, died in the attacks on subways and a bus on July 7.

The only suspected bomber in custody is Yasin Hassan Omar, 24, a Somali citizen who was arrested during a dramatic raid in Birmingham on Wednesday. He was being questioned yesterday in London.

In the Aswat case, a spokesman for the Foreign Office in London said diplomats are seeking consular access to an unidentified British national reported to be in custody in Zambia. Officials in Britain, Zambia and the United States who spoke on the condition of anonymity confirmed that the man in question is Aswat. The arrest was reported in yesterday's editions of the Los Angeles Times.

Masri, who is in British custody, is charged in connection with a variety of terrorism-related crimes, including a deadly hostage-taking in Yemen and efforts to set up a jihad training camp in Oregon.

Aswat was an aide to Masri, and officials have said he is listed as an "unindicted co-conspirator" in a related case against James Ujaama, an American who pleaded guilty to conspiring to aid the Taliban in Afghanistan and was also charged with planning to set up the Oregon camp. Ujaama has been interviewed by FBI agents in recent days about Aswat, officials have said.

Correspondent Glenn Frankel in London and staff writer Dafna Linzer in Washington contributed to this report.